Some vaccines tied to lower kids' leukemia risk

NEW YORK (Reuters Health) - Kids who have had certain vaccines might be less likely to develop cancer, especially one type of leukemia, suggests a new study.

The findings, published in The Journal of Pediatrics, showed that kids born in counties where most children had been vaccinated for hepatitis B had about 20 percent lower odds of all types of childhood cancers than those born in counties where fewer were vaccinated.

Those born in counties with high use both of polio vaccines and of a vaccine series that included hepatitis B and polio, among other diseases, had 30 to 40 percent lower odds of getting acute lymphoblastic leukemia, a cancer that affects the white blood cells.

But despite the apparent relationship, which should become more clear with future research, "we don't think it's the end all be all," said Dr. Michael Scheurer, one of the study's authors from the Baylor College of Medicine in Houston, Texas. It's not "get your kids vaccinated and they won't get cancer."

Previous studies of the subject have shown mixed results. According to one theory, some common infections may increase a child's risk of leukemia, or blood cancer, because of the effect they have on the developing immune system.

Vaccinations, theoretically, should then cut down on that cancer risk - unless the vaccine itself closely enough mimics a natural infection.

According the National Cancer Institute, more than 10,000 kids are diagnosed with cancer each year. The most common childhood cancers are leukemia and brain and spinal cord cancers.

Scheurer and his colleagues wanted to see if kids born in areas of Texas where most children were vaccinated according to standard procedures were more or less likely to get cancer than those born in areas with lower vaccination rates. Using data on all cancer diagnoses in the state, they identified 2,800 cases of childhood cancer diagnosed in 1995-2006 among kids born in Texas.

The authors focused on kids who were diagnosed when they were at least 2 years old, as vaccinations have generally been completed by then.

For each child who had been diagnosed with cancer, the researchers found four others of the same age and gender who had not. Then, they compared how many of the kids with and without cancer had been born in counties with high vaccination rates.

While the authors did not have data on which individual children had been vaccinated, kids living in areas with high vaccination rates are generally considered safe from infection because of "herd immunity" - the idea that infection can't spread when only a few are susceptible.

According to Scheurer, the strongest finding was a decreased risk of leukemia in areas with high vaccination rates for hepatitis B and polio - which is also where most of the previous childhood cancer research has shown a benefit for vaccination.

This particular study is timely, Scheurer said, because it coincides with recent news that British researcher Andrew Wakefield faked some of the scientific evidence that supposedly showed a link between vaccines and autism (see Reuters story of January 6, 2011).

After that, "people can take a step back and really look at the benefit that vaccines provide," Scheurer said, "not just for the infectious diseases that they were intended to prevent. Now, there appears to be some other added benefit" to vaccines.